In order to reduce carbon dioxide emission from vehicles, there is strong demand of improving fuel consumption so as to enhance utilization efficiency of energy. Recently, in addition to traditional vehicles that run by a conventional engine only, electric vehicles such as hybrid electric vehicles that combine an engine and a motor-generator and battery electric vehicles that run by a motor only, have appeared and such electric vehicles are rapidly becoming popular. In the electric vehicles, in addition to a conventional low-voltage battery which is a lead battery, a high-voltage battery, such as a nickel-hydride battery and a lithium-ion battery, is used for supplying power to the motor-generator.
In the electric vehicles, there is no electric generator (alternator), and instead, an insulated type DC-DC converter that takes an input from the high-voltage battery is used, which serves to supply power to the low-voltage battery (lead battery) and a low-voltage load that corresponds to conventional electrical components. As a conventional power conversion device that establishes connection between different voltage sides of the high-voltage battery and the low-voltage battery and low-voltage load, there has been provided a following device.
The conventional power conversion device includes a full-bridge switching circuit that is disposed between an input terminal and a transformer and that has first and second arms, an output circuit disposed between an output terminal and the transformer, and a control circuit that performs a phase shift control of the switching circuit. In the switching circuit, a diode and a capacitor are connected in parallel to each of switching elements, the midpoint of the first arm is connected to one end of the primary winding of the transformer through a resonant inductor, and the midpoint of the second arm is connected to the other end of the primary winding of the transformer.
The control circuit has a current detection unit for detecting pulse components that emerge in a primary-side current flowing between the input terminal and the switching circuit during an output non-delivery period, and a dead-time setting unit for changing a dead time for at least one of the first and second arms on the basis of the detection result by the current detection unit.